1. Field of the Invention
The present invention relates to a trackball device which is used, for example, as a device for moving a cursor on a display screen.
2. Description of the Related Art
Trackball devices have been proposed as X-Y coordinate input means for moving a cursor or the like on a display screen to a desired coordinate point, on the screen, or to select a desired menu item appearing on the display. Some trackball devices respond to manual rotation of a ball partly projecting from an upper wall of a casing.
FIG. 3 is a schematic perspective view of a major portion of a known trackball device. As will be seen from this Figure, this known trackball device has a housing 32 serving as an outer shell and provided with a circular opening formed in a top wall thereof, a ball received in the housing 32 and partially projecting through the circular opening 31, a pair of rotatable members 34, 35 which are arranged orthogonally to each other and which are rotatable in accordance with the rotation of the ball 33, and detectors 36, 37 such as encoders capable of detecting the amounts of rotation of the rotatable members 34, 35. The rotatable member 34 includes a roller 38 contacting a lower portion of the ball 33 and a rotary shaft 39 rotatable as a unit with the roller 38. The other rotatable member 35 has a similar construction.
In operation, the user rotates by hand the ball 33 projecting through the circular opening 31 in the casing 32. The X-axis component and the Y-axis component of the rotation are transmitted to the orthogonal rotatable members 34, 35. The amounts of rotation of these rotatable members 34 and 35 are respectively detected by detectors 36, 37 which produce detection signals in accordance with which a cursor is moved on a display screen (not shown) of a display device to which the trackball device is connected. When the cursor has been moved to a desired coordinate position or to a position of a desired menu item, the user stops the rotation of the ball 33 and turns an input switch (not shown) on thereby inputting the coordinate value or selecting the menu item.
Trackball devices of the kind described are finding spreading use and have been used as a component of a display device which is mounted on vehicles such as automobiles. The known trackball devices, when used on vehicles, encounter the following problems due to vibration of the vehicle. Namely, the ball vibrates up and down so as to collide with the edge 31a of the circular opening 31 in the housing 32 so as to generate chattering noise which annoys persons on board. In addition, the edge 31a tends to be damaged.